Data strobe signals are signals that are provided from a memory or provided to the memory when read data is output and write data is received by the memory, respectively. Data strobe signals are related to read and write data, but are not themselves data signals. For example, a read data strobe signal is provided by the memory and typically has signal transitions between a high and low levels that are coincident with the signal transitions between bits of read data output by the memory. A write data strobe signal is provided to the memory and typically has signal transitions that are coincident with “data eyes” of the bits of write data received by the memory. The write data strobe signal may be used by the memory to time the latching of the write data. Both read data and write data strobe signals typically include preamble and post amble portions that frame a strobe portion of the data strobe signals. The preamble portion may be used to establish a stable strobe condition just prior to use (either by the memory in the case of write data or a requesting entity in the case of read data) for example, at a rising edge of a next clock cycle. The post amble portions signal may be used to provide a clean strobe completion, for example, a low time after a falling edge used for data capture.
Read and write data strobe signals are typically provided from and received at a shared signal node. That is, the read data strobe is provided from a signal node during the output of data by the memory and the write data strobe is provided to the same signal node during receipt of write data by the memory. In situations where read and write operations occur immediately in sequence, a buffer coupled to the shared signal node must be allowed to conclude provision of, for example, the read data strobe and then prepare to receive, for example, the write data strobe without missing the beginning of the write strobe. In order to provide sufficient “turn around” time for the buffer, at least one clock period is typically inserted between the end of one data strobe signal and the beginning of the other data strobe signal. During the turn around time, no data can be provided or received by the memory. As a result, data bandwidth of the memory is negatively affected.
In addition to data strobe signals, other signals that are not data signals and that are not data strobe signals, but are related to read or write data may be received or provided by the memory. For example, a data mask DM signal may be provided to a memory receiving write data and used to mask portions of the write data written to memory. Another example is an output data valid QV signal which may be provided by the memory with the output of read data to indicate that the read data is valid and can be latched by a receiving entity. As known, there are other examples of non-data signals related to data as well.
Although not all examples of non-data signals are used in every memory application, memory designers often design a memory to include the functionality in order to provide flexibility in the use of the memory for various types of memory systems. As a result, the memory includes additional signal nodes to and from which non-data signals may be provided, thereby increasing the “pin count” for memories. Increasing memory pin count may be undesirable due to size constraints and board layout complexity resulting from the signal nodes, among other reasons. As the number of memory signals continues to increase, the difficulties associated with increasing memory pin count may increase as well.